U.S. patent application number 11/614376 was filed with the patent office on 2007-06-28 for water-based inks for ink-jet printing.
This patent application is currently assigned to KAO CORPORATION. Invention is credited to Toshiya Iwasaki, Shigeki Nagashima, Makoto Sakakibara.
Application Number | 20070144399 11/614376 |
Document ID | / |
Family ID | 37946079 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070144399 |
Kind Code |
A1 |
Nagashima; Shigeki ; et
al. |
June 28, 2007 |
WATER-BASED INKS FOR INK-JET PRINTING
Abstract
The present invention relates to [1] a water dispersion for
ink-jet printing containing an organic pigment having a bulk of 3.5
to 20 mL/g; [2] a water dispersion for ink-jet printing including
water-insoluble polymer particles containing a pigment having a
bulk of 3.5 to 20 mL/g; [3] a water dispersion for ink-jet printing
containing an organic pigment obtained by a
pulverization/classification treatment wherein the organic pigment
has D50 of 2 to 15 .mu.m and D90 of 60 .mu.m or less; [4] a
water-based ink for ink-jet printing containing the respective
water dispersions which is excellent in election reliability, image
density, image uniformity and rubbing resistance; and [5] a process
for producing the respective water dispersions.
Inventors: |
Nagashima; Shigeki;
(Wakayama, JP) ; Sakakibara; Makoto; (Wakayama,
JP) ; Iwasaki; Toshiya; (Wakayama, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KAO CORPORATION
Chuo-ku
JP
|
Family ID: |
37946079 |
Appl. No.: |
11/614376 |
Filed: |
December 21, 2006 |
Current U.S.
Class: |
106/31.6 |
Current CPC
Class: |
C09B 67/0002 20130101;
C09B 67/009 20130101; C09D 11/322 20130101 |
Class at
Publication: |
106/031.6 |
International
Class: |
C09D 11/02 20060101
C09D011/02; C09D 11/00 20060101 C09D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2005 |
JP |
2005-376590 |
Jul 10, 2006 |
JP |
2006-188981 |
Claims
1. A water dispersion for ink-jet printing comprising an organic
pigment having a bulk of 3.5 to 20 mL/g.
2. The water dispersion for ink-jet printing according to claim 1,
wherein the organic pigment is obtained by a
pulverization/classification treatment.
3. The water dispersion for ink-jet printing according to claim 1,
wherein the organic pigment has D50 (cumulative 50% value in
frequency distribution of scattering intensity when the cumulative
percentage is calculated sequentially from smaller particles) of 2
to 15 .mu.m, and D90 (cumulative 90% value in frequency
distribution of scattering intensity when the cumulative percentage
is calculated sequentially from smaller particles) of 60 .mu.m or
less.
4. A water dispersion for ink-jet printing comprising an organic
pigment obtained by a pulverization/classification treatment,
wherein the organic pigment has D50 (cumulative 50% value in
frequency distribution of scattering intensity when the cumulative
percentage is calculated sequentially from smaller particles) of 2
to 15 .mu.m, and D90 (cumulative 90% value in frequency
distribution of scattering intensity when the cumulative percentage
is calculated sequentially from smaller particles) of 60 .mu.m or
less.
5. A water dispersion for ink-jet printing comprising
water-insoluble polymer particles containing a pigment having a
bulk of 3.5 to 20 mL/g.
6. The water dispersion for ink-jet printing according to claim 5,
wherein the pigment is obtained by a pulverization/classification
treatment.
7. The water dispersion for ink-jet printing according to claim 5,
wherein the pigment has D50 (cumulative 50% value in frequency
distribution of scattering intensity when the cumulative percentage
is calculated sequentially from smaller particles) of 2 to 15
.mu.m, and D90 (cumulative 90% value in frequency distribution of
scattering intensity when the cumulative percentage is calculated
sequentially from smaller particles) of 60 .mu.m or less.
8. The water dispersion for ink-jet printing according to claim 5,
wherein the water-insoluble polymer particles containing the
pigment have D50 (cumulative 50% value in frequency distribution of
scattering intensity when the cumulative percentage is calculated
sequentially from smaller particles) of 70 to 120 nm, and D90
(cumulative 90% value in frequency distribution of scattering
intensity when the cumulative percentage is calculated sequentially
from smaller particles) of 90 to 180 nm.
9. The water dispersion for ink-jet printing according to claim 5,
wherein the water-insoluble polymer is a water-insoluble vinyl
polymer obtained by copolymerizing a monomer mixture containing a
salt-forming group-containing monomer (a), a macromer (b) and a
hydrophobic monomer (c).
10. The water dispersion for ink-jet printing according to claim 9,
wherein the hydrophobic monomer (c) is an alkyl methacrylate
containing a long-chain alkyl group having 8 to 30 carbon atoms
and/or an aromatic ring-containing monomer.
11. A water-based ink for ink-jet printing comprising the water
dispersion as defined in claim 1, 4 or 5.
12. A process for producing a water dispersion for ink-jet
printing, comprising the following steps (1) and (2): (1)
subjecting a pigment to a pulverization/classification treatment to
obtain a pigment having a bulk of 3.5 to 20 mL/g; and (2)
dispersing the pigment obtained in the step (1) in an aqueous
medium in the presence of a water-insoluble polymer to obtain
water-insoluble polymer particles containing the pigment.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to water dispersions for
ink-jet printing, water-based inks containing the water
dispersions, and a process for producing the water dispersions.
BACKGROUND OF THE INVENTION
[0002] In ink-jet printing methods, droplets of ink are directly
projected onto a recording medium from very fine nozzles and
allowed to adhere to the recording medium, to form characters and
images. The use of ink-jet printing methods have been rapidly
spread because of their various advantages such as easiness of full
coloration, low cost, capability of using plain paper as the
recording medium, non-contact with printed images and characters,
etc.
[0003] Among such printing methods, in view of enhancing the
weather resistance and water resistance of printed images and
characters, an ink-jet printing method utilizing an ink containing
a pigment as the colorant has now come to be the dominate method
(for example, refer to WO 00/39226, JP 2004-217905A and JP
11-12513A).
[0004] WO 00/39226 discloses a water-based ink containing a
pigment-containing vinyl polymer which is in the form of a graft
polymer obtained from a macromer to achieve a high optical density.
JP 2004-217905A discloses a water-based ink containing a water
dispersion of a water-insoluble vinyl polymer obtained by
copolymerizing a monomer mixture containing a salt-forming
group-containing monomer (a), a long-chain alkyl group-containing
monomer (b), a macromer (c), a polyoxyalkylene group-containing
monomer, etc.
[0005] JP 11-12513A discloses an ink prepared by dispersing carbon
black having a bulk density of 120 g/L or less, a water-soluble
resin having a weight-average molecular weight of 3000 to 20000
which is composed of a styrene-(meth)acrylic acid-(meth)acrylate
copolymer, a polyhydric alcohol and an aliphatic monohydric
alcohol, in water.
[0006] These conventional water-based inks are improved in image
density, etc., to some extent, but are still unsatisfactory, and it
is therefore desired to further improve these properties.
SUMMARY OF THE INVENTION
[0007] The present invention relates to the following aspects [1]
to [5]: [0008] [1] A water dispersion for ink-jet printing
containing an organic pigment having a bulk of 3.5 to 20 mL/g.
[0009] [2] A water dispersion for ink-jet printing including
water-insoluble polymer particles containing a pigment having a
bulk of 3.5 to 20 mL/g. [0010] [3] A water dispersion for ink-jet
printing containing an organic pigment obtained by a
pulverization/classification treatment wherein the organic pigment
has D50 of 2 to 15 .mu.m and D90 of 60 .mu.m or less. [0011] [4] A
water-based ink for ink-jet printing containing the water
dispersion as described in any one of the above aspects [1] to [3].
[0012] [5] A process for producing a water dispersion for ink-jet
printing, containing the following steps (1) and (2):
[0013] (1) subjecting a pigment to a pulverization/classification
treatment to obtain a pigment having a bulk of 3.5 to 20 mL/g;
and
[0014] (2) dispersing the pigment obtained in the step (1) in an
aqueous medium in the presence of a water-insoluble polymer to
obtain water-insoluble polymer particles containing the
pigment.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present invention relates to a water dispersion for
ink-jet printing which is excellent in ejection reliability, image
density, image uniformity and rubbing resistance, a water-based ink
containing the water dispersion, and a process for producing the
water dispersion.
[0016] The inventors have found that when using a pigment having a
specific bulk or a pigment having a specific particle size which is
obtained by a pulverization/classification treatment, the resultant
water dispersion is excellent in ejection reliability, image
density, image uniformity and rubbing resistance.
(Pigment)
[0017] The pigment used in the present invention preferably has a
bulk of 3.5 to 20 mL/g, more preferably 3.7 to 18 mL/g and even
more preferably 3.8 to 16 mL/g in view of attaining excellent
ejection reliability, image density, image uniformity and rubbing
resistance when blended in inks. The pigment usable in the present
invention is not particularly limited as long as the bulk thereof
lies within the above-specified range, and may be either organic or
inorganic. The pigment may also be a self-dispersible type pigment.
Further, the pigment may be used in combination with an extender
pigment, if required. The bulk of the pigment may be measured at
25.degree. C. according to JIS K5101-18(1978). In order to reduce
error upon the measurement, the bulk of the pigment is measured by
adjusting the water content thereof to 0.1% by weight or less.
[0018] Examples of the organic pigments include azo pigments,
disazo pigments, phthalocyanine pigments, quinacridone pigments,
isoindolinone pigments, dioxazine pigments, perylene pigments,
perinone pigments, thioindigo pigments, anthraquinone pigments and
quinophthalone pigments.
[0019] Examples of the preferred organic pigments include those
pigments having respective product numbers of C.I. Pigment Yellow,
C.I. Pigment Red, C.I. Pigment Violet, C.I. Pigment Blue, C.I.
Pigment Green, etc. Specific examples of the suitable organic
pigments include C.I. Pigment Yellow 13, 17, 74, 83, 97, 109, 110,
120, 128, 139, 151, 154, 155, 174, 180; C.I. Pigment Red 48, 57:1,
122, 146, 176, 184, 185, 188, 202; C.I. Pigment Violet 19, 23; C.I.
Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 16, 60; and C.I. Pigment
Green 7, 36.
[0020] Examples of the inorganic pigments include carbon blacks,
metal oxides, metal sulfides and metal chlorides. Among these
inorganic pigments, carbon blacks are preferably used for black
water-based inks. The carbon blacks may include furnace blacks,
thermal lamp blacks, acetylene blacks and channel blacks.
[0021] Examples of the extender pigment include silica, calcium
carbonate and talc.
[0022] In order to render the pigment self-dispersible, a necessary
amount of an anionic hydrophilic group such as a carboxyl group, a
sulfonic group and a phosphoric group or a cationic hydrophilic
group such as an ammonium group and an amino group may be
chemically bonded to a surface of the pigment directly or through
the other atomic group by a known method.
[0023] In view of ejection reliability, image uniformity, etc.,
upon chromatic color high-speed printing, the pigment is preferably
an organic pigment.
(Production of Pigment)
[0024] The method for producing the pigment used in the present
invention is not particularly limited. The pigment is preferably
produced by pulverization/classification treatment in which the
pigment is pulverized and then classified. For example, after
pulverizing the pigment by a jet mill, a turbo mill, etc., the
pulverized pigment may be classified in an air classifier such as a
micro-plex and a turbo classifier, thereby obtaining the aimed
pigment. In view of a high efficiency, the pigment is preferably
produced by using a pulverization-classifier capable of performing
pulverization and classification of the pigment at the same time.
More preferably, the pigment is produced by using a
pulverization-classifier with a drying function which is capable of
performing drying, pulverization and classification of the pigment
at the same time, since such an apparatus allows even a wet pigment
(wet cake) obtained by a wet method to be finely divided. The
pulverization/classification treatment enables the pigment having a
bulk of 3.5 to 20 mL/g to be produced with a high efficiency.
[0025] Examples of the pulverization-classifier include a fluidized
bed-type jet mill.
[0026] The fluidized bed-type jet mill includes, for example, those
mills that have the following structure or is operated based on the
following principle. That is, in the fluidized bed-type jet mill, a
pulverization chamber in which a plurality of jet nozzles are
disposed in an opposed relation to each other is provided in a
lower portion thereof, a high-speed gas jet injected from the jet
nozzles forms a fluidized bed of pigment particles supplied into
the pulverization chamber, and acceleration and mutual impingement
of the particles are repeated to finely divide the pigment
particles.
[0027] The number of jet nozzles disposed in the jet mill is not
particularly limited, and a plurality of jet nozzles, preferably 3
to 4 jet nozzles, are disposed in an opposed relation to each other
in view of a good balance between the air amount, the flow amount
and the flow rate, impingement efficiency of the particles,
etc.
[0028] The pulverization-classifier is preferably further provided,
above the pulverization chamber, with a classifying rotor for
collecting the pulverized small-size pigment particles which were
moved upwardly.
[0029] The thus pulverized particles obtained in the above
pulverization step which are classified with an upper limit of the
particle size (upper-limit classification) are directly subjected
to the next classification step, in particular, preferably
subjected to a lower-limit classification for removing too fine
particles therefrom. The upper-limit classified particles obtained
in the pulverization step are inhibited from suffering from
agglomeration of fine particles contained therein, so that the
lower-limit classification can be performed with a high
accuracy.
[0030] The frequency of the classification step to be conducted is
not limited to one time, and the classification step may be
repeated a plurality of times using different kinds of classifiers.
The classifiers are preferably provided with a classification rotor
which may be disposed in the direction either parallel with or
perpendicular to the vertical direction of the classifier. In order
to obtain the small-size pigment having a sharp particle size
distribution with a high efficiency, the classification rotor is
preferably disposed in the direction parallel with the vertical
direction of the classifier. In particular, the classifier used in
the present invention is preferably equipped with a classification
rotor rotatably supported on a driving shaft as a central axis
which is disposed in the vertical direction in a casing thereof,
and stationary helical guide vanes fixedly supported concentrically
to the driving shaft as the central axis which are disposed in a
classification zone around an outer periphery of the classification
rotor so as to be spaced apart from the outer periphery of the
classification rotor.
[0031] With the classifier of this type, the pulverized upper-limit
classified particles fed into the casing are moved downwardly along
the classification zone around the outer periphery of the
classification rotor while being guided by the helical guide vanes.
An interior of the classification rotor is communicated with the
classification zone through classification vanes provided on an
outer peripheral surface of the classification rotor. When the
pulverized particles are moved downwardly, the finer pigment
particles having a predetermined bulk which are entrained on a
classifying air are sucked and introduced into the inside of the
classification rotor. On the other hand, coarse particles which are
not entrained on the classifying air are continuously moved
downwardly by gravity along the classification zone without being
collected by the classification rotor, and then discharged from an
outlet port for coarse particles, and further pulverized again, if
required.
[0032] The particle size distribution and bulk of the pigment may
be readily controlled by the revolution number of such a
classification rotor. The classifier is preferably provided with
two classification rotors which rotatably disposed in one casing on
a common driving shaft as a central axis. The two classification
rotors are preferably individually rotated in the same
direction.
[0033] When two classification rotors are respectively disposed as
upper and lower stage rotors, it is possible to classify the
pigment with a higher accuracy by controlling the suction speed of
the classifying air and the rotating speed of the respective
classification rotors. For example, the ratio of the rotating speed
of the upper stage classification rotor to the rotating speed of
the lower stage classification rotor, i.e., the ratio of a flow
rate of the upper stage classifying air to a flow rate of the lower
stage classification air, is preferably substantially identical to
each other in view of attaining a high classification accuracy and
a good yield of the pigment.
[0034] Specific examples of the fluidized bed-type jet mill
equipped with a plurality of jet nozzles and classification rotors,
include the pulverizer described in JP 2002-35631A, and "TFG"
series and "AFG" series commercially available from Hosokawa Micron
Co., Ltd. Specific examples of the classifier include those
classifiers described in FIGS. 1 and 2 of JP 11-216425, FIG. 6 of
JP 2004-78063A and FIG. 1 of JP 2001-293438A, and "TSP" series,
"TTSP" series and "Counter Jet Mill" all commercially available
from Hosokawa Micron Co., Ltd.
[0035] Specific examples of the pulverization-classifier with a
drying function include the "Dry Meister" series commercially
available from Hosokawa Micron Co., Ltd. Among them, "Dry Meister
DMR" is preferred. In the "Dry Meister" classifier, the pigment fed
thereto is pulverized (dispersed) and simultaneously dried in the
pulverizing portion thereof, and then the dried pigment fine
particles which are controlled to a predetermined bulk in the
classification portion thereof are continuously discharged
therefrom. In this case, the particle size distribution of the
pigment may be controlled by suitably adjusting the rotating speed
of the classification rotor. The rotating speed of the
pulverization rotor is preferably from 3000 to 8000 rpm and more
preferably from 4000 to 7000 rpm, whereas the rotating speed of the
classification rotor is preferably from 1000 to 5000 rpm. Also, a
feed rate (wet cake feed rate) of the wet pigment (wet cake)
produced by a wet method is preferably from 1 to 50 kg/h.
[0036] The bulk of the thus obtained pigment is preferably from 3.5
to 20 mL/g, more preferably from 3.7 to 18 mL/g and even more
preferably from 3.8 to 16 mL/g. The pigment preferably has such a
configuration having a less anisotropy (less the difference between
the major axis diameter and minor axis diameter). In view of
ejection reliability, image density, image uniformity and rubbing
resistance when blended in inks, the pigment has D50 (cumulative
50% value in frequency distribution of scattering intensity when
the cumulative percentage is calculated sequentially from smaller
particles) of preferably 2 to 15 .mu.m, more preferably 3 to 12
.mu.m and even more preferably 5 to 10 .mu.m, and D90 (cumulative
90% value in frequency distribution of scattering intensity when
the cumulative percentage is calculated sequentially from smaller
particles) of preferably 60 .mu.m or less, more preferably 50 .mu.m
or less, even more preferably 30 .mu.m or less and even more
preferably 20 .mu.m or less, but preferably not less than 10 .mu.m.
Also, from the same viewpoints, the content of coarse particles
having a particle size of 20 .mu.m or more in the pigment (ratio of
number of coarse particles having a particle size of 20 .mu.m or
more in frequency distribution) is preferably 8% or less, more
preferably 6% or less, even more preferably 5% or less and even
more preferably 0%. The D50, D90 and content of coarse particles
having a particle size of 20 .mu.m or more may be measured by the
methods described in the below-mentioned Examples. The above
pulverization/classification treatment is advantageous in that the
resultant particles have the above suitable particle size
distribution unlike a filtration method in which particles having a
predetermined particle size or more are simply removed by a filter
without well-controlling a particle size distribution of the
resultant particles.
(Water-Insoluble Polymer)
[0037] The water dispersion and the water-based ink according to
the present invention are obtained by using a water dispersion
containing water-insoluble polymer particles in which the carbon
black is contained or incorporated, in view of attaining excellent
ejecting reliability and image density, etc.
[0038] Examples of water-insoluble polymer forming the
water-insoluble polymer particles include water-insoluble vinyl
polymers, water-insoluble ester-based polymers and water-insoluble
urethane-based polymers. Among these water-insoluble polymers,
preferred are water-insoluble vinyl polymers in view of good
stability of the resultant water dispersion.
[0039] The term "water-insoluble polymer" used herein means such a
polymer which is dissolved at 25.degree. C. in 100 g of water in an
amount of 10 g or less, preferably 5 g or less and more preferably
1 g or less after being dried at 105.degree. C. for 2 h. When the
water-insoluble polymer contains a salt-forming group, the above
amount of the water-insoluble polymer dissolved in water is
measured after the salt-forming group is neutralized 100% with
acetic acid or sodium hydroxide according to the kind of
salt-forming group.
[0040] The water-insoluble polymer is preferably a water-insoluble
graft polymer containing a constitutional unit derived from a
macromer (b) in view of allowing the resultant water dispersion and
water-based ink to exhibit a sufficient image density. In
particular, the water-insoluble polymer is more preferably a
water-insoluble graft polymer which includes a polymer unit
containing a constitutional unit derived from a salt-forming
group-containing monomer (a) and a constitutional unit derived from
a hydrophobic monomer (c) in a main chain thereof, and a polymer
unit containing a constitutional unit derived from the macromer (b)
in a side chain thereof.
[0041] The water-insoluble graft polymer is preferably a
water-insoluble vinyl polymer which may be produced by
copolymerizing a monomer mixture containing the salt-forming
group-containing monomer (a) (hereinafter occasionally referred to
merely as the "component (a)"), the macromer (b) (hereinafter
occasionally referred to merely as the "component (b)") and the
hydrophobic monomer (c) (hereinafter occasionally referred to
merely as the "component (c)") (hereinafter, the mixture is
occasionally referred to as merely a "monomer mixture").
Salt-forming Group-containing Monomer (a):
[0042] The salt-forming group-containing monomer (a) is used for
enhancing a dispersion stability of the resultant dispersion, etc.
The component (a) includes cationic monomers and anionic monomers.
Specific examples of the component (a) include those monomers
described on page 5, from column 7, line 24 to column 8, line 29 of
JP 9-286939A. Examples of the salt-forming group include a carboxyl
group, a sulfonic group, a phosphoric group, an amino group and an
ammonium group.
[0043] Typical examples of the cationic monomers include
unsaturated amine-containing monomers and unsaturated ammonium
salt-containing monomers. Among these cationic monomers, preferred
are N,N-dimethylaminoethyl (meth)acrylate and
N-(N',N'-dimethylaminopropyl) (meth)acrylate.
[0044] Typical examples of the anionic monomers include unsaturated
carboxylic acid monomers, unsaturated sulfonic acid monomers and
unsaturated phosphoric acid monomers.
[0045] Examples of the unsaturated carboxylic acid monomers include
acrylic acid, methacrylic acid, crotonic acid, itaconic acid,
maleic acid, fumaric acid, citraconic acid and
2-methacryloyloxymethylsuccinic acid.
[0046] Examples of the unsaturated sulfonic acid monomers include
styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,
3-sulfopropyl (meth)acrylate and bis(3-sulfopropyl)itaconate.
[0047] Examples of the unsaturated phosphoric acid monomers include
vinylphosphonic acid, vinyl phosphate,
bis(methacryloxyethyl)phosphate, diphenyl-2- acryloyloxyethyl
phosphate, diphenyl-2-methacryloyloxyethyl phosphate and
dibutyl-2-acryloyloxyethyl phosphate.
[0048] Among the above anionic monomers, in view of good dispersion
stability and good ejecting reliability of the resultant
dispersions and inks, preferred are the unsaturated carboxylic acid
monomers, and more preferred are acrylic acid and methacrylic
acid.
[0049] The above compounds as the component (a) may be used alone
or in combination of any two or more thereof.
Macromer (b):
[0050] The macromer (b) is used in view of enhancing a dispersion
stability of the water-insoluble polymer fine particles containing
the carbon black, etc., and may be such a macromer which is a
monomer containing a polymerizable unsaturated functional group at
one terminal end thereof and having a number-average molecular
weight of 500 to 100,000 and preferably 1,000 to 10,000.
[0051] Meanwhile, the number-average molecular weight of the
component (b) may be measured by gel permeation chromatography
using polystyrene as a standard substance and using tetrahydrofuran
containing 50 mmol/L of acetic acid as a solvent.
[0052] Specific examples of the macromer as the component (b)
include the below-mentioned styrene-based macromers (b-1), alkyl
(meth)acrylate-based macromers (b-2), aromatic ring-containing
(meth)acrylate-based macromers (b-3) and silicone-based macromers
(b-4).
Styrene-based Macromer (b-1):
[0053] The styrene-based macromer means a macromer containing a
constitutional unit derived from the styrene-based monomer
(hereinafter occasionally referred to merely as a "monomer (b-1)")
such as styrene, .alpha.-methyl styrene and vinyl toluene. Among
these styrene-based monomers, preferred is styrene.
[0054] Examples of the styrene-based macromer include styrene
homopolymers having a polymerizable functional group at one
terminal end thereof, and copolymers of styrene with the other
monomer which have a polymerizable functional group at one terminal
end thereof. The polymerizable functional group bonded to the one
terminal end is preferably an acryloyloxy group or a
methacryloyloxy group. When these functional groups are
copolymerized with the other components, it is possible to produce
the water-insoluble graft polymer containing a constitutional unit
derived from the styrene-based macromer.
[0055] Examples of the other monomer copolymerizable with styrene
include acrylonitrile, the below-mentioned (meth)acrylates
(hereinafter occasionally referred to merely as the "monomer
(b-2)"), and aromatic ring-containing (meth)acrylate-based monomers
other than styrene (hereinafter occasionally referred to merely as
the "monomer (b-3)").
[0056] The content of the constitutional unit derived from the
styrene-based monomer in the side chain or the styrene-based
macromer is preferably 60% by weight or more, more preferably 70%
by weight or more and even more preferably 90% by weight or more in
view of good rubbing resistance.
[0057] The styrene-based macromer is commercially available, for
example, from Toagosei Co., Ltd., as product names of AS-6(S),
AN-6(S), HS-6(S), etc.
Alkvl(meth)acrvlate-based Macromer (b-2)
[0058] The alkyl(meth)acrylate-based macromer means such a macromer
containing a constitutional unit derived from the (meth)acrylate
(hereinafter referred to merely as the "monomer (b-2)") containing
an alkyl group having 1 to 22 carbon atoms and preferably 1 to 18
carbon atoms which may also contain a hydroxyl group.
[0059] Specific examples of the (meth)acrylate include methyl
(meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate,
2-hydroxyethyl (meth)acrylate, (iso- or tertiary-)butyl
(meth)acrylate, 2-ethylhexyl (meth)acrylate, (iso)octyl
(meth)acrylate, (iso)decyl (meth)acrylate and (iso)stearyl
(meth)acrylate.
[0060] The side chain containing the constitutional unit derived
from the monomer (b-2) may be produced by copolymerizing the
alkyl(meth)acrylate-based macromer having a polymerizable
functional group at one terminal end thereof. Examples of the
alkyl(meth)acrylate-based macromer include a methyl
methacrylate-based macromer, a butyl acrylate-based macromer, an
isobutyl methacrylate-based macromer and a lauryl
methacrylate-based macromer.
[0061] These alkyl(meth)acrylate-based macromers may be
homopolymers of the alkyl(meth)acrylate having a polymerizable
functional group at one terminal end thereof, or copolymers of the
alkyl(meth)acrylate with other monomer which have a polymerizable
functional group at one terminal end thereof. The polymerizable
functional group bonded to one terminal end is preferably an
acryloyloxy group or a methacryloyloxy group. Examples of the other
monomer copolymerizable with the alkyl(meth)acrylate include the
above-mentioned styrene-based monomers (monomers (b-1)) and the
below-mentioned aromatic ring-containing (meth)acrylate-based
monomers other than styrene (monomer (b-3)).
[0062] In the side chain or the alkyl(meth)acrylate macromer, the
content of the constitutional unit derived from the (meth)acrylate
is largest, and preferably 60% by weight or more, more preferably
70% by weight or more and even more preferably 90% by weight or
more in view of good rubbing resistance.
Aromatic Ring-containing (meth)acrylate-based Macromer (b-3)
[0063] The aromatic ring-containing (meth)acrylate-based macromer
means such a macromer containing a constitutional unit derived from
the aromatic ring-containing (meth)acrylate as the monomer (b-3).
The aromatic ring-containing (meth)acrylate is preferably a monomer
represented by the following formula (2):
CH.sub.2=CR.sup.1COOR.sup.2 (2) wherein R.sup.1 is a hydrogen atom
or a methyl group; and R.sup.2 is a substituted or unsubstituted
arylalkyl group having 7 to 22 carbon atoms or a substituted or
unsubstituted aryl group having 6 to 22 carbon atoms.
[0064] Specific examples of the aromatic ring-containing
(meth)acrylate include benzyl (meth)acrylate, phenyl
(meth)acrylate, 2-phenylethyl (meth)acrylate, phenoxyethyl
(meth)acrylate, 1-naphthyl acrylate, 2-naphthyl (meth)acrylate,
phthalimidomethyl (meth)acrylate, p-nitrophenyl (meth)acrylate,
2-hydroxy-3-phenoxypropyl (meth)acrylate,
2-methacryloyloxyethyl-2-hydroxypropyl phthalate and
2-acryloyloxyethyl phthalate. Among these the aromatic
ring-containing (meth)acrylates, preferred is benzyl
(meth)acrylate. These aromatic ring-containing (meth)acrylates may
be used alone or in combination of any two or more thereof.
[0065] The side chain containing the constitutional unit derived
from the aromatic ring-containing (meth)acrylate may be produced by
copolymerizing the aromatic ring-containing (meth)acrylate -based
macromer having a polymerizable functional group at one terminal
end thereof.
[0066] Examples of the aromatic ring-containing
(meth)acrylate-based macromer include homopolymers of the aromatic
ring-containing (meth)acrylate having a polymerizable functional
group at one terminal end thereof, and copolymers of the aromatic
ring-containing (meth)acrylate with other monomer which have a
polymerizable functional group at one terminal end thereof. The
polymerizable functional group bonded to one terminal end of the
macromer is preferably an acryloyloxy group or a methacryloyloxy
group. Examples of the other monomers copolymerizable with the
aromatic ring-containing (meth)acrylate include the above-mentioned
styrene-based monomers as the monomer (b-1) and the (meth)acrylates
as the monomer (b-2).
[0067] In the side chain or the aromatic ring-containing
(meth)acrylate-based macromer, the constitutional unit derived from
the aromatic ring-containing (meth)acrylate has the largest
content.
Silicone-based Macromer (b-4)
[0068] The water-insoluble graft polymer used in the present
invention may further contain an organopolysiloxane chain as the
side chain thereof. Such a side chain is preferably produced, for
example, by copolymerizing a silicone-based macromer having a
polymerizable functional group at one terminal end thereof which is
represented by the following formula (3):
CH.sub.2=C(CH.sub.3)--COOC.sub.3H.sub.6--[Si(CH.sub.3).sub.2--O].sub.t--S-
i(CH.sub.3).sub.3 (3) wherein t is a number of 8 to 40.
[0069] When the polymer used in the present invention is the
water-insoluble graft polymer, the weight ratio of a main chain of
the polymer to a side chain thereof [main chain/side chain] is
preferably from 1/1 to 20/1, more preferably from 3/2 to 15/1 and
even more preferably from 2/1 to 10/1 in view of enhancing a
rubbing resistance and a storage stability. Meanwhile, the weight
ratio is calculated assuming that the polymerizable functional
group is contained in the side chain.
[0070] Among the above macromers, the styrene-based macromers
having a polymerizable functional group at one terminal end thereof
are preferred in view of a high affinity to the carbon black and an
enhanced storage stability.
Hydrophobic Monomer (c):
[0071] The hydrophobic monomer (c) is used for enhancing water
resistance, a high lighter-fastness, etc. Examples of the
hydrophobic monomer include alkyl (meth)acrylates, alkyl
(meth)acrylamides and aromatic ring-containing monomers.
[0072] The alkyl (meth)acrylates are preferably (meth)acrylates
containing an alkyl group having 1 to 30 carbon atoms. Examples of
the alkyl (meth)acrylates include methyl (meth)acrylate, ethyl
(meth)acrylate, (iso)propyl (meth)acrylate, (iso- or
tertiary-)butyl (meth)acrylate, (iso)amyl (meth)acrylate,
cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (iso)octyl
(meth)acrylate, (iso)decyl (meth)acrylate, (iso)dodecyl
(meth)acrylate, (iso)cetyl (meth)acrylate, (iso)stearyl
(meth)acrylate and (iso)behenyl (meth)acrylate. Among these alkyl
(meth)acrylates, in view of good dispersion stability, preferred
are (meth)acrylates containing a long-chain alkyl group having
preferably 8 to 30 carbon atoms and more preferably 12 to 22 carbon
atoms, and more preferred are (iso)lauryl (meth)acrylate,
(iso)stearyl (meth)acrylate and (iso)behenyl (meth)acrylate.
[0073] Examples of the alkyl (meth)acrylamides include
(meth)acrylamides containing an alkyl group having 1 to 22 carbon
atoms such as dimethyl (meth)acrylamide, diethyl (meth)acrylamide,
dibutyl (meth)acrylamide, t-butyl (meth)acrylamide, octyl
(meth)acrylamide and dodecyl (meth)acrylamide.
[0074] Examples of the aromatic ring-containing monomers include
styrene-based monomers (c-1) such as styrene, 2-methyl styrene and
vinyl toluene; aryl esters of (meth)acrylic acid such as benzyl
(meth)acrylate and phenoxyethyl (meth)acrylate; and aromatic
group-containing vinyl monomers having 6 to 22 carbon atoms (c-2)
such as ethyl vinyl benzene, 4-vinyl biphenyl, 1,1-diphenyl
ethylene, vinyl naphthalene and chlorostyrene.
[0075] Meanwhile, the terms "(iso- or tertiary-)" and "(iso)" used
herein mean both the structure in which the groups expressed by
"iso" and "tertiary" are present, and the structure in which these
groups are not present (namely, "normal"), and the term
"(meth)acrylate" means acrylate, methacrylate or both thereof.
[0076] As the component (c), in view of enhancing an image density
and a high lighter-fastness, there are preferably used the
(meth)acrylate containing a long-chain alkyl group having 8 to 30
carbon atoms and/or the aromatic ring-containing monomer.
[0077] The above respective components (c) may be used alone or in
combination of any two or more thereof.
(Other Monomers)
[0078] In the present invention, the monomer mixture containing the
respective components (a), (b) and (c) preferably further contains
(d) a hydroxyl-containing monomer (hereinafter occasionally
referred to merely as a "component (d)").
[0079] The component (d) exhibits an excellent effect of enhancing
the dispersion stability of the resultant dispersion. Examples of
the component (d) include 2-hydroxyethyl (meth)acrylate,
3-hydroxypropyl (meth)acrylate, polyethylene glycol (n=2 to 30
wherein n represents an average molar number of addition of
oxyalkylene groups: this definition is similarly applied to the
subsequent descriptions) (meth) acrylate, polypropylene glycol (n=2
to 30) (meth)acrylate and poly(ethylene glycol (n=1 to
15)/propylene glycol (n=1 to 15) (meth)acrylate. Among these
components (d), preferred are 2-hydroxyethyl (meth)acrylate,
polyethylene glycol monomethacrylate and polypropylene glycol
methacrylate.
[0080] The monomer mixture may further contain (e) a monomer
(hereinafter occasionally referred to merely as a "component (e)")
represented by the following general formula (4):
CH.sub.2=C(R.sup.3)COO(R.sup.4O).sub.pR.sup.5 (4) wherein R.sup.3
is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms;
R.sup.4 is a divalent hydrocarbon group having 1 to 30 carbon atoms
which may contain a hetero atom; R.sup.5 is a monovalent
hydrocarbon group having 1 to 30 carbon atoms which may contain a
hetero atom; and p represents an average molar number of addition,
and is a number from 1 to 60 and preferably a number from 1 to
30.
[0081] The component (e) exhibits an excellent effect of enhancing
an ejecting reliability of the resultant water-based ink and
preventing occurrence of slippage even upon continuous
printing.
[0082] In the general formula (4), examples of the hetero atom
which may be contained in R.sup.4 and R.sup.5 groups include a
nitrogen atom, an oxygen atom, a halogen atom and a sulfur
atom.
[0083] Typical examples of the groups represented by R.sup.4 and
R.sup.5 include an aromatic group having 6 to 30 carbon atoms, a
heterocyclic group having 3 to 30 carbon atoms, and an alkylene
group having 1 to 30 carbon atoms. These groups may have a
substituent group, and may be used in combination of any two or
more thereof. Examples of the substituent group include an aromatic
group, a heterocyclic group, an alkyl group, a halogen atom and an
amino group.
[0084] Examples of the groups represented by R.sup.4 include a
substituted or unsubstituted phenylene group having 1 to 24 carbon
atoms, an aliphatic alkylene group having 1 to 30 carbon atoms and
preferably 1 to 20 carbon atoms, an aromatic ring-containing
alkylene group having 7 to 30 carbon atoms, and a hetero
ring-containing alkylene group having 4 to 30 carbon atoms.
Specific examples of the preferred R.sup.4O group include an
oxymethylene group, an oxy(iso)propylene group, an
oxytetramethylene group, an oxyheptamethylene group, an
oxyhexamethylene group, oxyalkylene groups having 2 to 7 carbon
atoms which are each constituted from at least one of these
oxyalkylene groups, and an oxyphenylene group.
[0085] Examples of the groups represented by R.sup.5 include a
phenyl group, a branched or unbranched aliphatic alkyl group having
1 to 30 carbon atoms and preferably 1 to 20 carbon atoms, an
aromatic ring-containing alkyl group having 7 to 30 carbon atoms,
and a hetero ring-containing alkyl group having 4 to 30 carbon
atoms. Examples of the preferred R.sup.5 group include an alkyl
group having 1 to 12 carbon atoms such as methyl, ethyl,
(iso)propyl, (iso)butyl, (iso)pentyl and (iso)hexyl, and a phenyl
group.
[0086] Specific examples of the component (e) include methoxy
polyethylene glycol (p in the general formula (4): 1 to 30; this
definition is similarly applied to the subsequent descriptions)
(meth)acrylate, methoxy polytetramethylene glycol (p=1 to 30)
(meth)acrylate, ethoxy polyethylene glycol (p=1 to 30)
(meth)acrylate, (iso)propoxy polyethylene glycol (p=1 to 30)
(meth)acrylate, butoxy polyethylene glycol (p=1 to 30)
(meth)acrylate, octoxy polyethylene glycol (p=1 to 30)
(meth)acrylate, methoxy polypropylene glycol (p=1 to 30)
(meth)acrylate, and methoxy (ethylene glycol/propylene glycol
copolymer) (p=1 to 30: among which the number of ethylene glycol
constitutional units is 1 to 29) (meth)acrylate. Among these
compounds, preferred is methoxy polyethylene glycol (p=2 to 20)
(meth)acrylate and octoxy polyethylene glycol (p=2 to 20)
(meth)acrylate.
[0087] Specific examples of the commercially available components
(d) and (e) include polyfunctional acrylate monomers (NK Esters)
available from Shin-Nakamura Kagaku Kogyo Co., Ltd., such as
"M-40G", "M-90G" and "M-230G"; and BLEMMER Series available from
NOF Corporation, such as "PE-90", "PE-200", "PE-350", "PME-100",
"PME-200", "PME-400", "PME-1000", "PP-500", "PP-800", "PP-1000",
"AP-150", "AP-400", "AP-550", "AP-800", "50PEP-300" and
"50POEP-800B".
[0088] These components (d) and (e) are respectively used alone or
in the form of a mixture of any two or more thereof.
[0089] Upon production of the water-insoluble polymer, the
respective contents of the above components (a) to (e) in the
monomer mixture (contents of unneutralized components; this
definition is similarly applied to the subsequent descriptions) or
the contents of respective constitutional units derived from the
components (a) to (e) are as follows.
[0090] The content of the component (a) is preferably from 1 to 50%
by weight, more preferably from 2 to 40% by weight, even more
preferably from 3 to 30% by weight and further even more preferably
from 5 to 20% by weight in view of good dispersion stability of the
resultant dispersion, etc.
[0091] The content of the component (b) is preferably from 1 to 50%
by weight, more preferably from 3 to 40% by weight and even more
preferably from 5 to 35% by weight in view of good dispersion
stability of the resultant dispersion, etc.
[0092] The content of the component (c) is preferably from 5 to 90%
by weight, more preferably from 5 to 80% by weight and even more
preferably from 10 to 60% by weight in view of enhancing water
resistance, a high lighter-fastness, gloss, etc.
[0093] The weight ratio of the component (a) to a sum of the
components (b) and (c) ((a)/[(b)+(c)]) is preferably from 0.01 to
1, more preferably from 0.02 to 0.7 and even more preferably from
0.05 to 0.5 in view of a good long-term storage stability and good
ejecting reliability of the resultant water-based ink, etc.
[0094] The content of the component (d) is preferably from 1 to 40%
by weight, more preferably from 2 to 30% by weight and even more
preferably from 5 to 25% by weight in view of good
re-dispersibility and good dispersion stability.
[0095] The content of the component (e) is preferably from 1 to 50%
by weight, more preferably from 2 to 30% by weight and even more
preferably from 5 to 30% by weight in view of good ejecting
reliability, good dispersion stability, etc.
[0096] The total content of the components (a) and (d) in the
monomer mixture is preferably from 5 to 60% by weight, more
preferably from 7 to 50% by weight and even more preferably from 10
to 40% by weight in view of good stability in water and good water
resistance, etc.
[0097] The total content of the components (a) and (e) in the
monomer mixture is preferably from 5 to 75% by weight, more
preferably from 7 to 50% by weight and even more preferably from 10
to 40% by weight in view of good dispersion stability in water and
good ejecting reliability, etc.
[0098] The total content of the components (a), (d) and (e) in the
monomer mixture may be controlled, if required, to the range of
preferably from 5 to 60% by weight, more preferably from 7 to 50%
by weight and even more preferably from 10 to 40% by weight in view
of good dispersion stability in water, good ejecting reliability,
etc.
[0099] The water-insoluble polymer constituting the water-insoluble
polymer particles used in the present invention may be produced by
copolymerizing the monomer mixture by known methods such as bulk
polymerization, solution polymerization, suspension polymerization
and emulsion polymerization. Among these polymerization methods,
the solution polymerization is preferred since the effects such as
high image density and high anti-bleeding property are suitably
attained by the method.
[0100] The solvent used in the solution polymerization method is
preferably an organic polar solvent having a high affinity to the
water-insoluble polymer. The organic polar solvent preferably has a
solubility in water of not more than 50% by weight but not less
than 5% by weight as measured at 20.degree. C. Examples of the
organic polar solvents include aliphatic alcohols such as
butoxyethanol; aromatic hydrocarbons such as toluene and xylene;
ketones such as methyl ethyl ketone and methyl isobutyl ketone; and
esters such as ethyl acetate. Among these solvents, preferred are
methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene,
butoxyethanol, and mixed solvents of at least one thereof with
water.
[0101] The polymerization may be carried out in the presence of a
conventionally known polymerization initiator, e.g., azo compounds
such as 2,2'-azobisisobutyronitrile and
2,2'-azobis(2,4-dimethylvaleronitrile), and organic peroxides such
as t-butyl peroxyoctoate and dibenzoyl oxide. The amount of the
polymerization initiator to be used is preferably from 0.001 to 5
mol and preferably from 0.01 to 2 mol per 1 mol of the monomer
mixture.
[0102] The polymerization may also be carried out in the presence
of a conventionally known chain transfer agent, e.g., mercaptans
such as octyl mercaptan and 2-mercaptoethanol, and thiuram
disulfides.
[0103] The polymerization conditions of the monomer mixture vary
depending upon the kinds of polymerization initiators, monomers,
solvents, etc., to be used, and the polymerization is generally
conducted at a temperature of 30 to 100.degree. C. and preferably
50 to 80.degree. C. The polymerization time is from 1 to 20 h. The
polymerization is preferably conducted in an atmosphere of an inert
gas such as nitrogen and argon.
[0104] After completion of the polymerization, the polymer thus
produced may be isolated from the reaction solution by a known
method such as reprecipitation and removal of solvent by
distillation. The thus obtained polymer may be purified by repeated
reprecipitation, membrane separation, chromatography, extraction,
etc., for removing unreacted monomers, etc., therefrom.
[0105] The weight-average molecular weight of the resultant
water-insoluble polymer is preferably from 1,000 to 500,000, more
preferably from 5,000 to 400,000, even more preferably from 10,000
to 300,000 and further even more preferably from 14,000 to 200,000
in view of good dispersion stability of the carbon black, good
water resistance and good ejecting reliability.
[0106] Meanwhile, the weight-average molecular weight of the
polymer may be measured by gel permeation chromatography using
polystyrene as a standard substance and using chloroform containing
1 mmol/L of dodecyldimethylamine as a solvent.
[0107] When the water-insoluble polymer used in the present
invention contains a salt-forming group derived from the
salt-forming group-containing monomer (a), the salt-forming group
is neutralized with a neutralizing agent. As the neutralizing
agent, acids or bases may be used according to the kind of the
salt-forming group contained in the polymer. Examples of the
neutralizing agent include acids such as hydrochloric acid, acetic
acid, propionic acid, phosphoric acid, sulfuric acid, lactic acid,
succinic acid, glycolic acid, gluconic acid and glyceric acid, and
bases such as lithium hydroxide, sodium hydroxide, potassium
hydroxide, ammonia, methylamine, dimethylamine, trimethylamine,
ethylamine, diethylamine, triethylamine, triethanolamine and
tributylamine.
[0108] The degree of neutralization of the salt-forming group is
preferably from 10 to 200%, more preferably from 20 to 180% and
even more preferably from 50 to 150%. When the salt-forming group
is an anionic group, the degree of neutralization thereof is
calculated according to the following formula: [weight (g) of
neutralizing agent)/equivalent of neutralizing agent]/[acid value
of polymer (KOH mg/g).times.weight (g) of
polymer/(56.times.1000)].times.100
[0109] When the salt-forming group is a cationic group, the degree
of neutralization thereof is calculated according to the following
formula: [weight (g) of neutralizing agent)/equivalent of
neutralizing agent]/[amine value of polymer (HCl mg/g).times.weight
(g) of polymer/(36.5.times.1000)].times.100
[0110] The acid value or amine value may be calculated from the
respective constitutional units of the polymer, or may also be
determined by the method of subjecting a solution prepared by
dissolving the polymer in an appropriate solvent such as methyl
ethyl ketone to titration.
Process for Production of Water Dispersion
[0111] The water dispersion that contains the water-insoluble
polymer particles containing the pigment having a bulk of 3.5 to 20
mL/g or the water-insoluble polymer particles containing the
organic pigment obtained by the pulverization/classification
treatment (both are hereinafter referred to merely as
"pigment-containing particles") is obtained by dispersing the
pigment in an aqueous medium in the presence of the water-insoluble
polymer, and preferably produced through the following steps (1)
and (2):
[0112] Step (1): Dispersing a mixture containing the
water-insoluble polymer, the organic solvent, the above-prepared
pigment having a bulk of 3.5 to 20 mL/g or the organic pigment
obtained by the pulverization/classification treatment (both are
hereinafter occasionally referred to merely as "pigment"), and
water as well as neutralizing agent, if required.
[0113] Step (2): Removing the organic solvent from the resultant
dispersion.
[0114] In the step (1), first, preferably, the water-insoluble
polymer is dissolved in an organic solvent, and then the pigment
and water together with optional components such as neutralizing
agent and surfactant, if required, are added and mixed in the
resultant organic solvent solution to obtain a dispersion of an
oil-in-water type. The content of the pigment in the mixture is
preferably from 5 to 50% by weight. The content of the organic
solvent in the mixture is preferably from 10 to 70% by weight. The
content of the water-insoluble polymer in the mixture is preferably
from 2 to 40% by weight, and the content of water in the mixture is
preferably from 10 to 70% by weight. The water-insoluble polymer
containing a salt-forming group is preferably neutralized with a
neutralizing agent. In this case, the water-insoluble polymer may
be previously neutralized with the neutralizing agent. The degree
of neutralization of the salt-forming group in the polymer is not
particularly limited. In general, the degree of neutralization is
preferably controlled such that the finally obtained water
dispersion exhibits a neutral liquid property, for example, a pH of
4 to 10. The pH of the dispersion may also be determined from a
desired degree of neutralization for the water-insoluble
polymer.
[0115] Examples of the preferred organic solvents include alcohol
solvents, ketone solvents and ether solvents, i.e., the organic
solvents are preferably those having a solubility in water of not
more than 50% by weight but not less than 10% by weight as measured
at 20.degree. C.
[0116] Examples of the alcohol solvents include ethanol,
isopropanol, various butanols and diacetone alcohol. Examples of
the ketone solvents include acetone, methyl ethyl ketone, diethyl
ketone and methyl isobutyl ketone. Examples of the ether solvents
include dibutyl ether, tetrahydrofuran and dioxane. Among these
solvents, preferred are isopropanol, acetone and methyl ethyl
ketone, and more preferred is methyl ethyl ketone. These solvents
may be used alone or in the form of a mixture of any two or more
thereof.
[0117] As the neutralizing agent, there may be used the same
compounds as described above.
[0118] The method for dispersing the mixture used in the step (1)
is not particularly limited. Preferably, the mixture is first
subjected to preliminary dispersion procedure, and then to the
substantial dispersion procedure by applying a shear stress
thereto.
[0119] Upon subjecting the mixture to the preliminary dispersion
procedure, there may be used ordinary mixing or stirring devices
such as anchor blades. Examples of the preferred mixing or stirring
devices include high-speed mixers or stirrers.
[0120] To apply the shear stress to the mixture in the substantial
dispersion procedure, there may be used, for example, kneading
machines such as roll mills, beads mills, kneaders and extruders,
and homo-valve-type or chamber-type high-pressure homogenizers.
[0121] In the step (2), the organic solvent is removed by
distillation from the dispersion thus obtained in the above step
(1) to render the dispersion aqueous or water-based and thereby
obtain a water dispersion of the pigment-containing particles
having a desired average particle size. The removal of the organic
solvent from the water dispersion may be performed by an ordinary
method such as distillation under reduced pressure. The organic
solvent is substantially completely removed from the thus obtained
water dispersion of the pigment-containing particles. The content
of the residual organic solvent in the water dispersion is
preferably 0.1% by weight or less and more preferably 0.01% by
weight or less. Further, the thus obtained water dispersion of the
pigment-containing particles may be classified by centrifugal
separation in order to obtain the pigment-containing particles
having a desired particle size. The water dispersion of the
pigment-containing particles is preferably passed through a filter
to remove coarse particles therefrom. Although such coarse
particles are usually not present or present only in a small
amount, in order to prevent clogging of nozzles in a printer, the
mesh size of the filter is preferably from 0.45 to 10 .mu.m and
more preferably from 0.8 to 5 .mu.m.
[0122] In the above water dispersion of the pigment-containing
particles, solid components made of the pigment-containing
water-insoluble polymer are dispersed in water as a main medium.
The configuration of the pigment-containing particles is not
particularly limited as long as the particles are formed from at
least the pigment and the water-insoluble polymer. Examples of the
configuration of the pigment-containing particles include the
particle configuration in which the pigment is enclosed in the
respective water-insoluble polymer particles, the particle
configuration in which the pigment is uniformly dispersed in the
respective water-insoluble polymer particles, and the particle
configuration in which the pigment is exposed onto a surface of the
respective water-insoluble polymer particles.
[0123] The pigment-containing particles have D50 (cumulative 50%
value in frequency distribution of scattering intensity when the
cumulative percentage is calculated sequentially from smaller
particles) of preferably 120 nm or less, more preferably 115 nm or
less and even more preferably 110 nm or less, in view of prevention
of clogging of the nozzles in a printer, dispersion stability,
ejection reliability, image density, image uniformity and rubbing
resistance. The lower limit of D50 of the pigment-containing
particles is preferably 70 nm or more and more preferably 80 nm or
more in view of the facilitated production of the
pigment-containing particles. From the above viewpoints, the D50 of
the pigment-containing particles is more preferably from 70 to 120
nm, even more preferably from 80 to 115 nm and further even more
preferably from 80 to 110 nm.
[0124] The pigment-containing particles have D90 (cumulative 90%
value in frequency distribution of scattering intensity when the
cumulative percentage is calculated sequentially from smaller
particles) of preferably 180 nm or less, more preferably 170 nm or
less and even more preferably 160 nm or less, in view of less
content of coarse particles, enhanced storage stability of the
water dispersion, ejection reliability, image density, image
uniformity and rubbing resistance. The lower limit of D90 of the
pigment-containing particles is preferably 90 nm or more and more
preferably 100 nm or more in view of facilitated production of the
pigment-containing particles. From the above viewpoints, the D90 of
the pigment-containing particles is more preferably in the range of
from 90 to 180 nm, even more preferably from 100 to 170 nm and
further even more preferably from 100 to 160 nm.
[0125] The D50 and D90 of the pigment-containing particles may be
measured by the methods described in the Examples below.
[0126] The water dispersion of the water-insoluble polymer
particles may be directly used as a water-based ink using water as
a main medium, and may further contain various additives ordinarily
used in water-based inks for ink-jet printing such as wetting
agents, penetrants, dispersants, viscosity modifiers, defoaming
agents, mildew-proof agents and anti-corrosion agents.
[0127] The content of the pigment in the water dispersion and the
water-based ink of the present invention is preferably from 1 to
30% by weight, more preferably from 2 to 20% by weight, even more
preferably from 2 to 10% by weight and further even more preferably
from 3 to 8% by weight in view of good dispersion stability, a high
image density, etc. Also, the weight ratio of the pigment to the
water-insoluble polymer [pigment/water-insoluble polymer] is
preferably from 50/50 to 90/10 and more preferably from 50/50 to
80/20 in view of a high image density, etc.
[0128] The content (solid content) of the pigment-containing
particles in the water dispersion and the water-based ink is
preferably controlled to the range of from 0.5 to 30% by weight and
more preferably from 1 to 15% by weight in view of a high image
density and good ejection reliability thereof.
[0129] The content of water in the water dispersion and the
water-based ink of the present invention is preferably from 10 to
90% by weight and more preferably from 20 to 80% by weight.
[0130] The surface tension of the water dispersion of the present
invention is preferably from 30 to 65 mN/m and more preferably from
35 to 60 mN/m as measured at 20.degree. C., and the surface tension
of the water-based ink of the present invention is preferably from
25 to 50 mN/m and more preferably from 27 to 45 mN/m as measured at
20.degree. C.
[0131] The viscosity of the water dispersion of the present
invention which has a solid content of 20 wt % is preferably from 1
to 12 mPas, more preferably from 1 to 9 mPas and even more
preferably from 2 to 6 mPas as measured at 20.degree. C. to produce
a water-based ink having a suitable viscosity. The viscosity of the
water-based ink of the present invention is preferably from 2 to 20
mPas, more preferably from 2.2 to 15 mPas and even more preferably
from 2.2 to 12 mPas in view of maintaining good ejection
reliability thereof.
EXAMPLES
[0132] The following examples further describe and demonstrate
embodiments of the present invention. The examples are given solely
for the purpose of illustration and are not to be construed as
limitations of the present invention. In the following production
examples, examples and comparative examples, the "part(s)" and "%"
indicate "part(s) by weight" and "% by weight", respectively,
unless otherwise specified.
Production Examples 1 and 2
(Production of Polymer Solution)
[0133] A reaction vessel was charged with 40.1 parts (on the weight
basis) of a monomer solution as an initial charge shown in Table 1,
followed by mixing the solution. Then, the reaction vessel was
fully purged with a nitrogen gas to thereby obtain a mixed
solution.
[0134] Separately, 160.4 parts (on the weight basis) of a dropping
monomer solution as shown in Table 1 was charged into a dropping
funnel, and the dropping funnel was fully purged with a nitrogen
gas to thereby obtain a mixed solution.
[0135] The mixed solution in the reaction vessel was heated to
75.degree. C. while stirring in a nitrogen atmosphere, and then the
mixed solution in the dropping funnel was gradually dropped
thereinto over 3 h. After completion of the dropping, the obtained
mixed solution was held at a temperature of 75.degree. C. for 2 h,
and then a solution prepared by dissolving 0.3 part of a
polymerization initiator (2,2'-Azobis(2,4-dimethyl valeronitrile)
in 5 parts of methyl ethyl ketone was added to the mixed solution,
and the resultant solution was aged at 75.degree. C. for 3 h and
further at 85.degree. C. for 2 h to obtain a polymer solution.
[0136] A part of the resultant polymer solution was dried under
reduced pressure at 105.degree. C. for 2 h to remove the solvent
therefrom, thereby isolating the polymer. The weight-average
molecular weight of the resultant polymer was measured by the above
method.
[0137] The results are shown in Table 1. Meanwhile, the numerical
values of the respective monomers as shown in Table 1 indicate
weight parts of the effective ingredients therein. TABLE-US-00001
TABLE 1 Production Production Example 1 Example 2 Initially charged
monomer solution (wt part) (a) Methacrylic acid 3 3 (b) Styrene
macromer*.sup.1 2 2 (c) Styrene 10 2 (c) Stearyl methacrylate 10
(d) Polypropylene glycol monomethacrylate*.sup.2 3 (e) Octoxy
polyethylene glycol 5 monomethacrylate*.sup.3 Methyl ethyl ketone
20 20 2 -Mercaptoethanol 0.1 0.1 Dropping monomer solution (wt
part) (a) Methacrylic acid 12 12 (b) Styrene macromer*1 8 8 (c)
Styrene 40 8 (c) Stearyl methacrylate 40 (d) Polypropylene glycol
monomethacrylate*.sup.2 12 (e) Octoxy polyethylene glycol 20
monomethacrylate*.sup.3 Methyl ethyl ketone 80 80 2-Mercaptoethanol
0.1 0.1 2,2'-Azobis(2,4-dimethyl valeronitrile) 0.3 0.3
Weight-average molecular weight of resultant 38,000 51,000 polymer
Note: *.sup.1"AS-6S" (tradename) having a number-average molecular
weight of 6000 available from Toagosei Co., Ltd. *.sup.2"PP-500"
(tradename) available from NOF Corporation; molar number of
addition of propyleneoxide: 9 mol in average; terminal group:
hydrogen *.sup.3Development product available from Shin-Nakamura
Kagaku Kogyo Co., Ltd.; molar number of addition of ethyleneoxide:
4 mol in average; terminal group: 2-ethylhexyl
Examples 1 to 4 and Comparative Examples 1 and 2
(Water Dispersion of Pigment-Containing Particles, and Production
of Water-Based Ink)
[0138] Twenty five parts of the polymer obtained by drying the
polymer solution produced in Production Examples 1 and 2 under
reduced pressure, was dissolved in 71 parts of methyl ethyl ketone,
and a neutralizing agent (5N sodium hydroxide aqueous solution) was
added to the obtained polymer solution in an amount of 65% (7
parts) on the basis of an acid value thereof, and simultaneously
211 parts by weight of ion-exchanged water was added thereto while
stirring to neutralize a salt-forming group of the polymer.
Further, 75 parts by weight of the below-mentioned pigment was
added to the neutralized product, and the resultant mixture was
fully stirred and then dispersed under a high pressure of 180 MPa
by passing through a dispersing apparatus "MICROFLUIDIZER"
(tradename) available from Microfluidics Corp., 15 times, thereby
obtaining water-insoluble vinyl polymer particles enclosing the
colorant.
[0139] The resultant paste was diluted (about 10%) with
ion-exchanged water, fully stirred, and then heat-treated using an
evaporator to remove methyl ethyl ketone and water therefrom,
thereby obtaining a water dispersion of pigment-containing
particles having a solid content of 20%. The average particle size
of the thus obtained pigment-containing particles was measured by
the below-mentioned method. The results are shown in Table 2.
[Pigment]
[0140] The following pigments were used in Examples 1 to 4 and
Comparative Examples 1 and 2.
[0141] A dimethyl quinacridon pigment (C.I. Pigment Red 122;
available from Ciba Specialty Chemicals Inc.; tradename: "IRGAPHOR
MAGENTA DMQ Crude") was processed under the following conditions
using "Dry Meister DNR-1" available from Hosokawa Micron Co.,
Ltd.
[0142] Pigment 1 used in Example 1: Pulverized and classified at an
injection drying temperature of 150.degree. C.; a wet cake feed
rate of 47 kg/h; a classification rotor vent temperature of 67 to
74.degree. C.; a pulverization rotor rotating speed of 5000 rpm; a
classification rotor rotating speed of 1000 rpm; and a
dust-collecting air flow rate of 25 Nm.sup.3/min.
[0143] Pigment 2 used in Example 2: Pulverized and classified in
the same manner as Pigment 1 except for using a wet cake feed rate
of 30 kg/h; a pulverization rotor rotating speed of 5500 rpm; and a
classification rotor rotating speed of 3000 rpm.
[0144] Pigment 3 used in Example 3: Pulverized and classified in
the same manner as Pigment 1 except for using a wet cake feed rate
of 20 kg/h; a pulverization rotor rotating speed of 5500 rpm; and a
classification rotor rotating speed of 4000 rpm.
[0145] Pigment 4 used in Example 4: Pulverized and classified in
the same manner as Pigment 1 except for using a wet cake feed rate
of 10 kg/h; a pulverization rotor rotating speed of 6200 rpm; and a
classification rotor rotating speed of 5000 rpm.
[0146] Pigment 5 used in Comparative Example 1: Untreated dimethyl
quinacridon pigment (C.I. Pigment Red 122).
[0147] Pigment 6 used in Comparative Example 2: The untreated
dimethyl quinacridon pigment (C.I. Pigment Red 122) was dried, and
then pulverized for 1 h at a pulverization rotor rotating speed of
2200 rpm using "Pulverizer ACM-100" available from Hosokawa Micron
Co., Ltd.
[Measurement of Particle Size of Pigment]
[0148] Measured using a laser diffraction/scattering type particle
size distribution measuring apparatus ""LA-950" (dry type & wet
type) available from Horiba Seisakusho Co., Ltd., under the
following conditions.
[0149] Temperature: 25.degree. C.; Dispersing Medium: Ethanol;
Circulation Level: 5; Stirring Level: 1
[0150] No ultrasonic dispersion was conducted, and a refractive
index (1.36) of ethanol was inputted as a refractive index of the
dispersing medium, and the value of 1.60 was inputted as a
refractive index of the organic substance.
[Measurement of Particle Size of Pigment-Containing Particles]
[0151] Measured using a laser particle analyzing system "ELS-8000"
(cumulant analysis) available from Otsuka Denshi Co., Ltd., under
the following conditions.
[0152] Temperature: 25.degree. C.;
[0153] Angle between incident light and detector: 90.degree.;
[0154] Cumulative frequency: 200 times
[0155] A refractive index of water (1.333) was inputted to the
analyzing system as a refractive index of the dispersing medium.
Upon the above measurement, a concentration of the solution to be
measured was about 5.times.10.sup.-3% by weight.
[0156] Twenty five parts of the above obtained water dispersion of
the pigment-containing particles, 10 parts of glycerol, 5 parts of
2-{2-(2-butoxyethoxy)ethoxy}ethanol, 2 parts of hexanediol, 0.5
part of acetylene glycol EO adduct (n=10) ["ACETYLENOL E100"
(tradename) available from Kawaken Fine Chemical Co., Ltd.] and
57.5 parts of ion-exchanged water were mixed with each other. The
resultant mixed solution was passed through a 1.2-.mu.m membrane
filter "Minisart (tradename)" available from Sartorius Inc.,
thereby obtaining a water-based ink.
[0157] The properties of water-based inks obtained in the
respective Examples and Comparative Examples were evaluated by the
following methods. The results are shown in Table 2.
(1) Ejection Reliability
[0158] Using an ink-jet printer "EM930C" (product number) of a
piezoelectric type commercially available from Seiko Epson Co.,
Ltd., after character images were continuously printed at a rate of
2000 characters per sheet on 100 plain papers P "4024" available
from Fuji Xerox Co., Ltd., a text document including characters,
solid images and ruled lines was printed on the paper to evaluate
the following three items:
[0159] (i) Sharp and clear characters;
[0160] (ii) Uniform solid images; and
[0161] (iii) No slippage of ruled lines.
[0162] The results were evaluated according to the following
evaluation criteria.
[Evaluation Criteria]
[0163] .largecircle.: All of the three items were satisfied
(Acceptable level);
[0164] .DELTA.: The three items were not completely but almost
satisfied (Still acceptable level without practical problem);
and
[0165] X: One or more items were unsatisfied (Not acceptable
level).
(2) Image Density
[0166] Solid image printing was carried out on the same plain paper
P "4024" as used in the above (1). After allowing the printed paper
to stand for one day, the image density was measured at optional 10
positions on the paper using an optical densitometer "SpectroEye"
available from Gretag-Macbeth Corp., to calculate an average of the
measured values.
(3) Image Uniformity (Voids)
[0167] Solid image printing was carried out on the same plain paper
P "4024" as used in the above (1) to conduct a sensory evaluation
about whether or not any unevenness of color occurred. The results
were evaluated according to the following evaluation criteria.
[Evaluation Criteria]
[0168] .largecircle.: No unevenness of color occurred (No
voids);
[0169] .DELTA.: Some unevenness of color occurred; and
[0170] X: Significant unevenness of color occurred (Voids).
(4) Rubfastness:
[0171] Solid image printing was carried out on the same plain paper
P as used in the above (1) and a chromatic color glossy paper
available from Fuji Xerox Co., Ltd., and dried at 25.degree. C. for
24 h. Then, the printed surface of each paper was strongly rubbed
with fingers to evaluate the degree of rubbing-off of the printed
images according to the following evaluation criteria.
[Evaluation Criteria]
[0172] .largecircle.: Substantially no rubbing-off of printed
images, and no staining of surrounding portions.
[0173] .DELTA.: Substantially no rubbing-off of printed images and
slight staining of surrounding portions, but acceptable level
without practical problem.
[0174] X: Considerable rubbing-off of printed images, and severe
staining of surrounding portions and considerable staining of
fingers. TABLE-US-00002 TABLE 2 Comparative Examples Examples 1 2 3
4 1 2 Production Production Example of polymer 1 2 2 2 1 2 Pigment
Kind Pigment Pigment Pigment Pigment Pigment Pigment -1 -2 -3 -4 -5
-6 Bulk (mL/g) 4.0 6.0 8.0 12.0 2.0 3.2 D50 (.mu.m) 12.8 8.5 6.2
5.1 41.2 21.5 D90 (.mu.m) -- 17.4 16.1 -- 62.5 67.5 Content of 7 3
0 0 81 53 coarse particles having a particle size of 20 .mu.m or
more (wt %) Pigment-containing polymer particles Dispersed 107 106
98 88 128 108 particle size D 50 (nm) Dispersed 151 149 144 132 284
194 particle size D 90 (nm) Ejection .smallcircle. .smallcircle.
.smallcircle. .smallcircle. x .DELTA. reliability Image density
1.08 1.15 1.17 1.20 0.99 1.02 Image .smallcircle. .smallcircle.
.smallcircle. .smallcircle. x .DELTA. uniformity Rubfastness
.smallcircle. .smallcircle. .smallcircle. .smallcircle. x
.DELTA.
[0175] From Table 2, it was confirmed that the water-based inks
obtained in Examples 1 to 4 were excellent in ejection reliability,
image density, image uniformity and rubbing resistance as compared
to the water-based inks obtained in Comparative Examples 1 and 2.
Further, it was confirmed that the water-based inks of the present
invention were excellent in re-dispersibility.
[0176] The water-based ink containing the water dispersion for
ink-jet printing according to the present invention is excellent in
ejection reliability, image density, image uniformity and rubbing
resistance. The water-based ink of the present invention can be
suitably used in high-speed printing operation using an ink-jet
printing method.
* * * * *